Hardening mechanisms and recrystallization behaviour of several molybdenum alloys

The present study describes the effect of thermomechanical treatments on the microstructure of molybdenum–titanium and the molybdenum alloy TZM (0.5 wt.% Ti, 0.08 wt.% Zr). These alloys were processed by a powder metallurgical route including extensive rolling at temperatures above 1200 °C achieving deformation degrees of 2.87 (logarithmic). The alloys exhibit a distinct increase in yield stress without decreasing elongation at fracture. To study the recrystallization behaviour, several samples were annealed at temperatures between 1100 °C and 1600 °C for 15 min until 6 h. The microstructure was examined by scanning electron microscopy (SEM), electron backscattering diffraction (EBSD) and transmission electron microscopy (TEM). Strain rate controlled tensile tests and Vickers hardness measurements are used to determine the mechanical properties. In both alloys a distinct substructure containing subgrains is formed during deformation. A kind of (sub)grain refinement was considered to be responsible for hardening. Present particles are able to raise the recrystallization temperature and thus sustain the grain size effects even at working temperatures above 1200 °C.